Automatic battery charging regulator for emergency lighting and power systems

ABSTRACT

A voltage sensing circuit monitors the battery voltage and places the battery on &#39;&#39;&#39;&#39;fast charge&#39;&#39;&#39;&#39; rate through a silicon controlled rectifier, when the monitored battery voltage drops to a predetermined value. When the battery has charged to a certain value, the battery is automatically returned to a &#39;&#39;&#39;&#39;trickle charge&#39;&#39;&#39;&#39; rate through a parallel circuit. A clamping circuit maintains the circuit in &#39;&#39;&#39;&#39;trickle&#39;&#39;&#39;&#39; charge condition until the battery voltage is again sensed to have fallen below the first aforementioned desired predetermined value preventing &#39;&#39;&#39;&#39;hunting&#39;&#39;&#39;&#39; of the battery by providing control with a voltage differential between the &#39;&#39;&#39;&#39;trickle&#39;&#39;&#39;&#39; and &#39;&#39;&#39;&#39;fast&#39;&#39;&#39;&#39; charging rates.

United States Paten Bembenek [54] AUTOMATIC BATTERY CHARGING REGULATORFOR EMERGENCY LIGHTING AND POWER SYSTEMS 51 Apr. 25, 1972 PrimaryExaminerWilliam M. Shoop, Jr. AttorneyArnold J. De Angelis [57] ABSTRACTA voltage sensing circuit monitors the battery voltage and places thebattery on fast charge rate through a silicon controlled rectifier, whenthe monitored battery voltage drops to a predetermined value. When thebattery has charged to a certain value, the battery is automaticallyreturned to a trickle charge rate through a parallel circuit. A clampingcircuit maintains the circuit in trickle charge condition until thebattery voltage is again sensed to have fallen below the firstaforementioned desired predetermined value preventing hunting of thebattery by providing control with a voltage differential between thetrickle and fast" charging rates.

7 Claims, 1 Drawing Figure All Patented April 25, 1972 3,659,181

L2 TRS SCRZ SCRB EDWARD BEMBENEK INVENTOR.

ATTORNEY.

AUTOMATIC BATTERY CHARGING REGULATOR FOR EMERGENCY LIGHTING AND POWERSYSTEMS The invention relates to voltage sensing circuits for monitoringthe voltage level of a voltage source and more particularly, to such acircuit for use as a battery charging regulator.

Battery charging voltage regulators usually provide for removing thecharging current when the battery voltage rises to full charge andautomatically applying charging current when the battery falls belowfull charge level.

Batteries used for emergency power, in present day practice are usuallymaintained on line in a stand by condition, while a trickle charge isconstantly being applied to the battery to maintain it at apredetermined level. When normal power fails, and an emergency load isapplied to the battery, the battery begins to discharge, causing itsvoltage to drop slowly. When the battery voltage drops to a certainlevel below the aforementioned trickle charge maintenance voltage, avoltage sensing circuit places the regulation circuit in condition forcharging of the battery at a relatively fast rate when normal power isrestored. Under such conditions, upon restoration of power, the batteryis fast charged to a fully charged condition. Upon the battery attainingfully charged condition, a voltage sensing circuit places the battery onthe slow trickle charge again to prevent gassing and evaporation of theelectrolyte which may lead to premature battery failure.

It is, therefore, desirable to provide in a battery charging regulatorcircuit of the voltage sensing type, a voltage differential control toprovide a positive transfer from a fast charge rate to a trickle chargerate with sufficient differential between transfer points to preventhunting of the regulator at near the fully charged voltage of thebattery source, while obtaining latching of the regulator in tricklecharge condition until the battery again falls below a predeterminedlevel.

In carrying out the invention, according to a preferred embodiment, upontransfer of the voltage sensing circuit which monitors the voltagesource from a fast charge rate condition to a trickle charge ratecondition, clamping means responsive to such transfer clamp the voltagesensing means in trickle charge condition, providing for actuation tofast charge condition at a voltage substantially lower than the tricklevoltage condition of the voltage source.

Features and advantages of the invention will be seen from the above andfrom the following description of the preferred embodiment, whenconsidered in conjunction with the drawing and from the appended claims.

In the drawing, there is a schematic wiring diagram of a stand byvoltage source in the form of battery B being maintained under tricklecharge condition by an automatic battery charging regulator embodyingthe invention.

The voltage source to be monitored is a battery B connected to outputterminals L3,L4 for supplying emergency or stand by power to a load (notshown). Power is supplied to the battery charging circuit from anyconvenient alternating current source (not shown) over supply linesL1,L2 at, say approximately 120 volts, 60 cycles. This power istransformed by transformer TRS and rectified by full wave rectifier Vconnected across the secondary winding of the transformer to applyrectified power at approximately 49 volts to the circuit.

The rectified power is usually applied across battery B at a tricklecharge rate, the circuit extending from the output of full wave bridgerectifier V through a diode D1 and an adjustable resistor R3 foradjusting the rate of charge. Fast charging of the battery isaccomplished through the anode-cathode circuit of a silicon controlledrectifier SCRl connected in shunting relation to diode D1 and resistorR3. The gate of rectifier SCRl is connected through a diode D2 to themidpoint of a voltage divider comprising resistors R8,R9. Theseresistors are in series with each other in the anode-cathode circuit ofanother silicon controlled rectifier SCR2 to provide a series circuitconnected across the output of rectifier V and in parallel with theaforementioned charging circuits for controlling firing of rectifierSCRl, as will be later explained. Diode D2 prevents false firing ofrectifier SCRl due to small voltage transients.

The voltage sensing and monitoring circuit for battery B includes afixed resistor R5 and an adjustable resistor R2 in series therewithacross the terminals of battery B, a capacitor C connected acrossselected portions of resistor R2 by means of an adjustable tap on theresistor, a zener diode Z1 connected from the adjustable tap of resistorR2 to the gate of silicon controlled rectifier SCR2 for controllingfiring of rectifier SCR2 when a selected voltage is sensed acrossbattery B. A biasing resistor R10 connects the gate electrode ofrectifier SCR2 to its cathode electrode.

A circuit for clamping zener diode Z1 in its avalanched conditionincludes a transistor Q1 with its base electrode connected to a voltagedivider circuit comprising resistors R6,R7 connected in series from thepositive terminal of battery B in the anode circuit of a third siliconcontrolled rectifier SCR3, whose cathode electrode is connected to thenegative terminal of battery B. The gate electrode of rectifier SCR3 isconnected directly to the gate electrode of the second siliconcontrolled rectifier SCR2 in the voltage sensing circuit to cause slavedfiring of rectifier SCR3 when rectifier SCR2 is caused to fire andconduct. The emitter electrode of transistor O1 is connected by anadjustable tap to a resistor R1 which is connected in series with afixed resistor R4 to the junction of the voltage sensing resistornetwork RS,R2 with the positive terminal of battery B.

The collector electrode of transistor O1 is connected directly to theadjustable tap on voltage sensing resistor R2 where it interconnectswith zener diode 21.

In a test of the preferred embodiment battery charging at a fast ratewas effected when the battery voltage dropped to approximately 32 volts.The battery was transferred to a trickle charge rate upon attaining 42volts, the trickle rate voltage applied being approximately 39 volts.The following circuit components were used to provide this broad voltagedifferential control of fast rate charge and trickle charge: RectifierSCRl was selected of the C37 F type, while rectifiers SCR2 and SCR3 wereselected C6F type. Transistor Q1 was selected of the 2N4037 type, whilezener diode Z1 was selected of the ITl6 type. Diodes D1 and D2 were ofthe IN2484 type. Capacitor C was selected of microfarads. The followingvalues of resistors were used:

R1 5 Kilo ohms R6 10 Kilo ohms R2 15 Kilo ohms R7 22 Kilo ohms R3 500ohms R8 & RN) 1 Kilo ohms R4 & R5 200 ohms R9 350 ohms In operationassume that alternating power from any convenient source (not shown) atapproximately volts is applied over supply lines L1,L2 to the circuitryunder conditions where battery B is not called upon to supply stand bypower to the load (not shown). Under such conditions, battery B is beingcharged at trickle rate through diode D1 and adjustable resistor R3,from step down transformer TRS and rectifier V, resistor R3 beingadjusted to an ohmic value to reduce the rectified power applied to thebattery to approximately 39 volts.

The previsously referred to fast charge rate circuit extending throughthe anode-cathode circuit of rectifier SCRl is in off condition, sincerectifier SCRl is maintained in nonconducting condition as follows: Withbattery B maintained at approximately 39 volts under a trickle chargeresistor R2 in the battery voltage sensing circuit is adjusted toprovide approximately 16 volts to zener diode Z1. This causes zenerdiode Z1 to avalanche and apply a firing signal to the gate electrode ofsilicon controlled rectifier SCR2. Silicon controlled Rectifier SCR2fires and conducts through its anode-cathode circuit, causing currentflow through resistors R8 and R9 in its anode circuit. With rectifierSCR2 conducting, resistors R8 and R9 essentially constitute a voltagedivider directly across the output terminals of full wave rectifier V.The value of resistors R8, R9, previously stated, are selected toreverse bias the gate electrode of silicon controlled rectifier SCRl inthe fast charge circuit under conditions where battery monitoringrectifier SCR2 is in conducting condition. Hence, with the batteryvoltage sensed to be 39 volts fast charge silicon controlled rectifierSCRl is maintained in its off condition, (nonconducting) preventing fastcharging of battery B through its anodecathode circuit.

Under the assumed trickle charge condition of the circuit with rectifierSCR2 in conducting condition its slaved rectifier SCR3 also is caused toconduct simultaneously therewith. In conducting rectifier SCR3 providesa current path through its anode-cathode circuit extending through avoltage divider resistors R6 and R7 and across battery B. The value ofresistor R1 is adjusted with relation to the impedance in the basecircuit of transistor Q1 to cause transistor O1 to conduct through itsemitter-collector circuit under these conditions. Transistor Q1, uponconducting, applies a low impedance shunt path through resistors R1,R4across the resistor network (R5,R2) connected to zener diode 21 therebyclamping a reference voltage greater than 16 volts directly to the zenerdiode under conditions where the battery voltage is approximately 39volts. This clamping voltage maintains the circuit in trickle chargecondition by preventing the removal of the firing signal from the gatesof silicon controlled rectifiers SCR2 and SCR3 through zener diode Z1until the voltage monitoring circuit senses approximately 32 voltsacross the battery terminals, as will now be explained.

Next assume that the 120 volts alternating power applied to supply linesL1, L2 fails and an emergency load (not shown) is connected to outputterminals L3,L4 of battery B. Feeding the load causes battery B todischarge, causing its terminal voltage to drop slowly. Assume that thebattery voltage drops to approximately 32 volts. Under such conditionsthe voltage monitored by the battery voltage sensing circuit and appliedto the zener diode Z1 through resistors R1,R4 and transistor Q1 drops tobelow the holding voltage of the zener diode, which holding voltage isapproximately 16 volts. Zener diode Z1 stops conducting, removing thefiring signal from the gates of silicon controlled rectifiers SCR2 andSCR3. As rectifier SCR3 ceases to conduct, transistor O1 is placed backto nonconducting condition, removing the shunt path across resistors R5and R2 in the monitoring circuit. As rectifier SCR2 ceases to conduct, afiring signal is applied through resistor R8 and diode D2 to the gate ofsilicon controlled rectifier SCRl. Rectifier SCRl conducts, placing alow impedance shunt path through the rectifier directly across thetrickle charge circuit of diode D1 and resistor R3, thereby placingbattery B in condition for charging at a fast rate upon the resumptionof the applied 120 volt power. Thus, the charging circuit is placedautomatically in condition for the fast charge of the battery.

Next assume that the normal 120 volt power is reapplied and theemergency load is removed from the output terminals L3,L4 of battery B.Under such conditions battery B, as has been explained, is automaticallycharged at a fast rate through the prepared anode-cathode circuit ofconducting rectifier SCRl. As battery B approaches its fully chargedcondition, the voltage across its output terminals rises. When thisvoltage approaches approximately 42 volts, battery B is considered fullycharged. Any further charging, while not resulting in any significantvoltage rise, will cause evaporation of the battery electrolyte andgassing of the battery. Potentiometer R2 is adjusted to apply areference voltage of approximately 16 volts to zener diode Z1, when thebattery voltage rises to approximately 42 volts. As was previouslyexplained, this causes zener diode Z1 in the battery voltage monitoringcircuit to avalanche, placing a firing signal on the gate electrodes ofrectifiers SCR2 and SCR3, again placing them in conducting condition.Rectifier SCR2, upon conducting, by means of current flow through thevoltage divider network R8,R9 in its anode circuit places fast chargerate rectifier SCRl in nonconthrough diode D1 and resistor R3. RectifierSCR3, upon conducting, causes current fiow through resistors R7,R6 inthe base circuit of transistor Q1, causing it to conduct through itsemitter-collector circuit, as was previously explained placing aclamping voltage higher than 16 volts to zener diode 21.

It may be noted that transistor 01, upon conducting, places resistorsR1,R4 across resistor R5 and a portion of resistor R2 lowering theimpedance of that voltage divider at the take off point for zener diodeZ1. This effectively reduces the total resistance and, thus causes ahigh reference voltage to be applied to zener diode Z1. This allowsbattery B to return to its trickle charge rate voltage, say 39 volts,while zener diode Z1 continues to see a voltage greater than 16 volts.The circuit is therefore, maintained in its avalanched condition. Thus,this clamping circuit maintains zener diode Z1 in conducting conditionand the charging circuit in trickle charge rate at 39 volts with nohunting or excessive gassing of the battery until the battery falls toapproximately 32 volts upon being placed across the load as waspreviously described.

It may be noted that without the clamping circuit of rectifier SCR3,resistor network R6,R7 R1 and R4 and transistor O1 to maintain zenerdiode Z1 clamped at above 16 volts, as the battery attains full chargetowards 42 volts, zener Z1 would conduct, causing rectifier SCRl to stopconducting, removing the fast charging circuit. However, under theseconditions, (without the clamping voltage to zener 21 applied bytransistor Q1) within seconds the battery voltage would again drop tobelow 42 volts. The voltage sensing circuit would again sense this dropapplying less than 16 volts to zener diode Z1. The diode Z1 would againconduct, stopping conduction of rectifier SCR2 and causing firing andconducting of SCRl to reapply the fast charging rate through battery B.This would result in hunting of the battery charging circuit from fastcharge to trickle charge with resultant damage to battery B. Thus, itcan be seen that the subject battery regulating and charging circuit ischaracterized by a means for clamping the charger in trickle chargecondition with an adjustable substantial voltage differential controlbetween initiation of the fast charging rate and termination of the fastcharging rate for return to trickle condition.

As changes can be named in the above described construction manyapparently different embodiments of this invention can be made withoutdeparting from the scope thereof, it is intended that all matter in theabove description or shown on the accompanying drawing be interpreted asillustrative only and not in a limiting sense.

What is claimed is:

1. For a battery supplying power selectively to a load,

a source of unidirectional power,

a first charging circuit including impedance means connecting saidbattery across said power source for charging at a predetermined slowrate,

a second charging circuit including switching means for selectivelyapplying a low impedance shunt path across said first charging circuitfor causing a relatively much faster charging rate of said battery,

circuit means for monitoring the voltage across said battery terminals,

said monitoring circuit means being actuated from a first condition to asecond condition in response to voltage at said terminals decreasing tobelow at least a predetermined level,

said monitoring circuit means being actuated from said second conditionto said first condition in response to voltage to said terminalsincreasing a certain amount above said predetermined level,

said second charging circuit being responsive to actuation of saidmonitoring circuit means from said first condition to said secondcondition for applying said low impedance shunt path across said firstcharging circuit for increasing charging rate of said battery to saidfaster rate,

characterized in that there are provided,

means includes,

clamping means responsive to actuation of said monitoring means back tosaid first condition for applying a signal to said monitoring means of acharacter for maintaining said monitoring means in said first conditionpreventing operation of said shunt path under conditions where saidfirst charging circuit is operatively charging said battery.

3. The circuit arrangement of claim 2 wherein,

said shunt switching means includes a silicon controlled rectifierhaving its anode-cathode circuit in shunting relation to said firstcharging circuit for applying a low impedance shunt path across it underconducting conditions of said rectifier.

4. The circuit of claim 3 wherein,

said battery monitoring circuit includes an adjustable voltage dividernetwork connected across said battery terminals, and

a second silicon controlled rectifier with its gate electrode connectedto a selected point on said voltage divider network, and with itscathode-anode circuit across said power source for placing said secondrectifier in conducting condition when said monitored battery terminalvoltage increases said certain amount above said predetermined level,and

wherein the gate electrode of said first silicon controlled rectifier isconnected to the anode circuit of said second silicon controlledrectifier for maintaining said first silicon controlled rectifier innonconducting condition under conditions where said second siliconcontrolled rectifier conducts through its anode-cathode circuit.

5. The circuit of claim 4 wherein said monitoring means includesavalanching means connecting said gate electrode of said secondrectifier to said voltage divider network for applying a firing signalto said second rectifier when said monitored voltage increases abovesaid predetermined level.

6. The circuit of claim 5 wherein,

said clamping means is responsive to conduction of said second siliconcontrolled rectifier for applying an increased voltage to saidavalanching means for maintaining said avalanching means at a certainamount above its avalanching value for maintaining said circuit in slowcharging condition under conditions where said power source maintainssaid battery terminal voltage at least at said certain amount above saidpredetermined level.

7. The circuit of claim 6 wherein,

said clamping means includes a transistor and interconnecting circuitmeans responsive to conduction of said second silicon controlledrectifier for placing said transistor in conducting condition when saidsecond silicon controlled rectifier conducts for applying a lowimpedance path across a selected portion of said voltage divider networkfor increasing the magnitude of the voltage signal applied to saidavalanching means for clamping said avalanching means in avalanchedcondition with a voltage signal a predetermined amount above itsavalanching value.

1. For a battery supplying power selectively to a load, a source ofunidirectional power, a first charging circuit including impedance meansconnecting said battery across said power source for charging at apredetermined slow rate, a second charging circuit including switchingmeans for selectively applying a low impedance shunt path across saidfirst charging circuit for causing a relatively much faster chargingrate of said battery, circuit means for monitoring the voltage acrosssaid battery terminals, said monitoring circuit means being actuatedfrom a first condition to a second condition in response to voltage atsaid terminals decreasing to below at least a predetermined level, saidmonitoring circuit means being actuated from said second condition tosaid first condition in response to voltage to said terminals increasinga certain amount above said predetermined level, said second chargingcircuit being responsive to actuation of said monitoring circuit meansfrom said first condition to said second condition for applying said lowimpedance shunt path across said first charging circuit for increasingcharging rate of said battery to said faster rate, characterized in thatthere are provided, voltage differential means responsive to actuationof said monitoring means to said first condition for providing aselected differential of said monitored voltage for actuating saidmonitoring means to said second condition.
 2. The circuit of claim 1wherein said voltage differential means includes, clamping meansresponsive to actuation of said monitoring means back to said firstcondition for applying a signal to said monitoring means of a characterfor maintaining said monitoring means in said first condition preventingoperation of said shunt path under conditions where said first chargingcircuit is operatively charging said battery.
 3. The circuit arrangementof claim 2 wherein, said shunt switching means includes a siliconcontrolled rectifier having its anode-cathode circuit in shuntingrelation to said first charging circuit for applying a low impedanceshunt path across it under conducting conditions of said rectifier. 4.The circuit of claim 3 wherein, said Battery monitoring circuit includesan adjustable voltage divider network connected across said batteryterminals, and a second silicon controlled rectifier with its gateelectrode connected to a selected point on said voltage divider network,and with its cathode-anode circuit across said power source for placingsaid second rectifier in conducting condition when said monitoredbattery terminal voltage increases said certain amount above saidpredetermined level, and wherein the gate electrode of said firstsilicon controlled rectifier is connected to the anode circuit of saidsecond silicon controlled rectifier for maintaining said first siliconcontrolled rectifier in nonconducting condition under conditions wheresaid second silicon controlled rectifier conducts through itsanode-cathode circuit.
 5. The circuit of claim 4 wherein said monitoringmeans includes avalanching means connecting said gate electrode of saidsecond rectifier to said voltage divider network for applying a firingsignal to said second rectifier when said monitored voltage increasesabove said predetermined level.
 6. The circuit of claim 5 wherein, saidclamping means is responsive to conduction of said second siliconcontrolled rectifier for applying an increased voltage to saidavalanching means for maintaining said avalanching means at a certainamount above its avalanching value for maintaining said circuit in slowcharging condition under conditions where said power source maintainssaid battery terminal voltage at least at said certain amount above saidpredetermined level.
 7. The circuit of claim 6 wherein, said clampingmeans includes a transistor and interconnecting circuit means responsiveto conduction of said second silicon controlled rectifier for placingsaid transistor in conducting condition when said second siliconcontrolled rectifier conducts for applying a low impedance path across aselected portion of said voltage divider network for increasing themagnitude of the voltage signal applied to said avalanching means forclamping said avalanching means in avalanched condition with a voltagesignal a predetermined amount above its avalanching value.